1. Field of the Invention
The invention relates to a camera that uses an objective lens through a thick prism, and particularly to a camera that has a thick prism and a corrector optic for reduction of image defects and restoration of image quality.
2. Discussion of the Related Art
A conventional camera that uses an objective lens in combination with a thick color-separation prism, where the objective-lens was designed for imaging through air, typically creates images that have quality detriments due to aberrations caused by the prism. A digital camera that uses three imagers for three color channels may use such a lens and prism for imaging, and thus may be subject to such image degradation. It is possible, as known in the prior art, to design lenses specifically to work through such a prism, such that the overall optical system of lens plus prism has sufficient image quality. That approach, however, does not allow a camera user or manufacturer to select from the wide range of commercially available, standard, removable lenses. Thus, it is desirable to provide, for a camera that uses conventional commercial camera lenses and a thick color-separation or beam-splitting prism, a means for restoring image.
A corrector optic is provided to be optically disposed between a prism and an objective lens of a camera, to improve the quality of images that are created by operation of the objective lens through the prism. A camera and an optical module are each provided; each includes a corrector optic comprising at least two lenses for compensating aberrations generated by the prism.
In further aspects of the invention, the corrector optic includes separate positive and negative lenses, for jointly correcting spherical and coma aberrations generated by the prism; the first lens is a positive lens having convex surface toward the objective lens, and the second is a negative lens having a concave surface toward the prism. The prism may be a thick color-separation prism or a beam-splitter prism. A corrector-optic module may be configured to mount to an objective-lens assembly and to a prism module, or the corrector optic may be contained within the prism module.